1. Technical Field
The present invention relates to a method for manufacturing an acceleration sensing unit, particularly an acceleration sensing unit in which the same piezoelectric material is used for a stress sensing element and an element supporting member, the element supporting member supports the stress sensing element and deforms when stress is applied, and an etching method is used to form the acceleration sensing unit.
2. Related Art
Acceleration sensors have been widely used for cars, airplanes and rockets, abnormal vibration monitoring systems in plants and the like. JP-A-2-248866 is an example of related art. Referring to FIG. 14, the example discloses a beam structure in an acceleration sensor. In FIG. 14 which is the perspective view of the beam structure, the reference number 90 denotes a double-ended tuning-fork type quartz crystal resonator having two resonating beams 91, the reference number 92 denotes an adhesion part of the double-ended tuning-fork type quartz crystal resonator 90, and the reference number 100 denotes a beam that is formed of the quartz crystal whose cut angle is the same as that of the quartz crystal forming the double-tuning fork type quartz crystal resonator 90. A protrusion part 110 which is a part of the beam 100 where contacts with the adhesion part 92 of the double-ended tuning-fork type quartz crystal resonator 90 and has a thickness larger than other part of the beam 100 is provided. The protrusion part 110 is formed so as to have a single body with the beam 100. The protrusion part 110 and the adhesion part 92 of the double-tuning fork type quartz crystal resonator are adhesively bonded and fixed together with adhesive or the like. A weight 120 is further provided on a free end of the beam 100 and the other end opposing the weight 120 is fixed onto a base 130.
The base 130 of the acceleration sensor described with reference to FIG. 14 is fixed on a measured object. When acceleration is given in the direction pointed by the arrow in the drawing, the weight 120 bends the beam 100 and the frequency of the double-ended tuning-fork type quartz crystal resonator 90 which is fixed on the beam 100 is changed due to compression or tensile stress. In other words, this is a sensor measuring the acceleration velocity which can be derived from a variation in the frequency. When the protrusion part 110 is provided on the beam 100, the stress applied to the double-ended tuning-fork type quartz crystal resonator 90 is increased compared with the case where the protrusion part 110 is not provided. In this way the example concludes that it is possible to form a highly sensitive acceleration sensor without increasing the thickness of the beam 100 and without increasing the mass of the weight 120.
However the weight is situated at the end of the beam in the acceleration sensor according to the example, the beam deformation due to the acceleration concentrates around the fixed part and does not sufficiently works throughout the double-ended tuning-fork type quartz crystal resonator. Moreover, the stress caused by the acceleration tends to be dispersed because the thickness of the beam is uniform. Consequently the deformation is less likely to occur with a small acceleration and there is a problem that the measurement accuracy falls insufficient with the small acceleration. In addition, there is another problem that the mass productivity of the sensor is low because each component is individually fabricated according to the example.